Subscriber station for a serial bus system and method for communicating in a serial bus system

ABSTRACT

A subscriber station for a serial bus system. The subscriber station has a communication control device for controlling a communication of the subscriber station with at least one other subscriber station of the bus system, a transmitting/receiving device for transmitting a transmission signal in a frame on a bus of the bus system, and a scheduling unit for scheduling a temporal access of the subscriber station to the bus in at least one time slot of a cycle of temporally consecutive time slots, at least one time slot being provided in a cycle for each subscriber station for transmitting its transmission signal and the cycle repeating cyclically. The scheduling unit is designed to determine an assignment that specifies which time slot of the cycle the transmitting/receiving device is allowed to use for transmitting the frame for the transmission signal on the bus.

FIELD

The present invention relates to a subscriber station for a serial bussystem and to a method for communicating in a serial bus system, whichallow for communication in real time critical applications.

BACKGROUND INFORMATION

For communication between sensors and control units, for example invehicles, a bus system is used ever more frequently, instead of apoint-to-point connection, for reasons of costs, data being transmittedin the bus system as messages by CAN FD in the ISO 11898-1:2015 standardas the CAN protocol specification. The messages are transmitted betweenthe subscriber stations of the bus system such as sensors, controlunits, transmitters, etc. Currently, CAN FD is used in the introductoryphase in the first step usually at a data bit rate of 2 MBit/s in thetransmission of bits of the data field and at an arbitration bit rate of500 kbit/s in the transmission of bits of the arbitration field in thevehicle.

To prevent collisions of messages of different subscriber stations onthe bus, CAN uses the CSMA/CR method (CR=collision resolution).Collisions are thereby resolved using a so-called arbitration at thebeginning of a message or a frame. In the arbitration, an identifier(ID) is evaluated to determine which message may be transmitted next. Inthe process, the message or frame prevails whose identifier has thehighest priority. This corresponds to strict priority scheduling. Thissuffices for many applications in the autonomous vehicle.

The arbitration has the effect, however, that current CAN-based bussystems cannot be used for cases of application that require a 100%deterministic bus access, that is, a guarantee that a subscriber stationof the bus system is definitely able to transmit a message or a frame ata certain time.

SUMMARY

It is an object of the present invention to provide a subscriber stationfor a serial bus system and a method for communicating in a serial bussystem, which resolve the aforementioned problems. In particular, asubscriber station for a serial bus system and a method forcommunication are to be provided, which are usable in a communicationfor real time critical applications and in which in particular a 100%deterministic bus access is possible.

The object may be attained by a subscriber station for a serial bussystem in accordance with an example embodiment of the presentinvention. In accordance with an example embodiment of the presentinvention, the subscriber station has a communication control device forcontrolling a communication of the subscriber station with at least oneother subscriber station of the bus system, a transmitting/receivingdevice for transmitting a transmission signal generated by thecommunication control device in a frame on a bus of the bus system, anda scheduling unit for scheduling a temporal access of the subscriberstation to the bus in at least one time slot of a cycle of temporallyconsecutive time slots, at least one time slot being provided in a cyclefor each subscriber station of the bus for transmitting its transmissionsignal and the cycle repeating cyclically, and the scheduling unit beingdesigned to determine, by using at least one item of informationreceived from the bus, an allocation that specifies which time slot ofthe cycle the transmitting/receiving device may use for transmitting theframe for the transmission signal on the bus.

In a bus system, to which the subscriber stations described above areconnected, it is ensured that every subscriber station isdeterministically able to access the bus. Consequently, each of thesubscriber stations receives a guaranteed minimum communicationbandwidth on the bus at least for the time, during which the bus is tobe accessed deterministically. This makes it possible to implementreal-time critical applications using even a CAN-based bus system.

The subscriber station may be used with any communication protocol thatoperates in accordance with the CSMA/CR method, for example with anyCAN-based communication protocol, in particular, however, with CAN XL, aCAN FD successor.

In the example subscriber station, it is also very advantageous that itis possible to activate the function of the deterministic scheduling forthe deterministic bus access, as needed, even in continuous operation.The subscriber station is thus designed to carry out two differentcommunication methods, namely, to carry out either a CSMA/CR method,which implements “strict priority scheduling”, or a CSMA/CR method withadditional deterministic scheduling. This is a great advantage comparedto bus systems, in which respectively only one of the mentionedcommunication methods is possible, such as for example 10BASE-TIS,Flexray, etc. A further very great advantage is that the approachdescribed here is considerably simpler in terms of configuration and usethan previous methods.

The described subscriber station in accordance with an exampleembodiment of the present invention is designed in such a way that ititself organizes, together with the other subscriber stations on thebus, which subscriber station may transmit the next message. Theconfiguration of the subscriber station and of the associated bus systemis thus self-organizing. This makes the configuration very simple toaccomplish. As a result, there is hardly any additional personneltraining required for configuring the bus system and the subscriberstation.

An additional advantage of the subscriber station is the fact that no“single point of failure” is possible, as is the case in the master noderequired for 10BASE-T1S. That is to say, when a subscriber station failsdue to a defect and therefore no longer transmits anything, this has nonegative effects on the communication on the bus.

Depending on the implemented variant of the deterministic scheduling,the subscriber station may provide either the same maximum delays (worstcase delays) as PLCA of 10BASE-T1S or maximum delays (worst case delays)that are shorter by approximately 50% than PLCA of 10BASE-T1S.

Additionally, it is possible to extend the subscriber station, dependingon the application or desire, with many additional functions, since thearbitration is always available. For transmission, it is possible forexample to make use of an unused time slot of another subscriber stationof the bus system. It is also possible to implement a weighted cyclicaltransmission (weighted round robin), in which some subscriber stationsare allowed to transmit more messages per cycle or round than othersubscriber stations. Another option is for a subscriber station of thebus system to be able to transmit in its time slot during a cycle alsomultiple shorter messages instead of one message of maximum length. Thisallows for fairness regarding the bandwidth available on the bus,instead of merely with regard to the number of messages transmitted ortransmittable by each subscriber station.

As a consequence, the subscriber station can be used to implement atransmission and reception of messages with great flexibility withregard to bus access, and thereby a very great range of quality ofservice requirements and thus applications may be realized.

Advantageous further developments of the subscriber station inaccordance with the present invention are disclosed herein.

The at least one item of information received from the bus is possibly aframe informing of the start of the cycle, the at least one item ofinformation received from the bus additionally comprising a frameidentifier and/or an assignment of the time slots of a cycle to thesubscriber stations of the bus and/or the information as to which of thesubscriber stations of the bus is currently transmitting.

According to one exemplary embodiment of the present invention, thescheduling unit is designed to use, as the at least one item ofinformation received from the bus, at least the frame informing of thestart of the cycle and to evaluate a frame identifier of a transmitterof a frame received from the bus.

According to another exemplary embodiment of the present invention, thescheduling unit is designed to evaluate a data field of the frameinforming of the start of the cycle, in which the at least one item ofinformation received from the bus is contained.

According to yet another exemplary embodiment of the present invention,the scheduling unit is designed to wait until the communication controldevice has received a frame informing of the start of the cycle from thebus, and subsequently to determine, together with the other subscriberstations of the bus in the operation of the bus system by using apriority of the transmission signal, which time slot of the cycle thetransmitting/receiving device may use for transmitting the frame for thetransmission signal on the bus.

It is possible for the communication control device to be designed topartition the frame, at least in a power up phase of the bus, into afirst communication phase and a second communication phase, it beingnegotiated in the first communication phase, which of the subscriberstations of the bus obtains an at least temporarily exclusive,collision-free access to the bus in the subsequent second communicationphase.

It is possible that the number of time slots per cycle is greater thanthe number of time slots assigned to the subscriber stations of the busper cycle, it being negotiated in the first communication phase in atime slot that is not assigned to a subscriber station of the bus, whichof the subscriber stations of the bus gains at least temporarilyexclusive, collision-free access to the bus in the subsequent secondcommunication phase.

Optionally, the minimum duration of a time slot may be selected as a bittime of a bit of the first communication phase. Optionally, thescheduling unit is designed to transmit, in a time slot assigned to thesubscriber station, a frame with a priority that is higher than apriority of a frame, which the scheduling unit is designed to transmitin a time slot that is assigned to another subscriber station of thebus.

Alternatively, it is possible that the minimum duration of a time slotis two bit times of a bit of the first communication phase, thescheduling unit being designed to approve a temporal access of thesubscriber station to the bus in the second bit of a time slot of thecycle, if the subscriber station or another subscriber station of thebus in the first bit of the time slot lets its transmission opportunityelapse unused.

According to a special variant of an embodiment of the presentinvention, the scheduling unit has a counting module, which is designedto increment its count value with every frame received from the bus andto increment it with every transmission opportunity for a time slot thatelapsed unused, the counting module being designed to set its countvalue to 1 if the frame informing of the start of the cycle wasreceived.

In this case, the counting module may be designed to increment its countvalue with every frame received from the bus following the reception ofa bit, which signals the beginning of a frame, even if the frame islater aborted by the subscriber station transmitting the frame due to anerror. In this case, the scheduling unit may be designed to approve atemporal access of the subscriber station on the bus for the next timeslot of the cycle, if the count value of the counting module is equal tothe number of the time slot assigned to the subscriber station.

According to one exemplary embodiment of the present invention, thescheduling unit is designed to approve a temporal access of thesubscriber station to the bus in a time slot of the cycle if anothersubscriber station of the bus lets its transmission opportunity elapseunused.

The communication control device may be designed to include in thetransmission signal a subscriber station number, which on the bus isexclusively assigned to the subscriber station, the scheduling unitbeing designed to approve a temporal access of the subscriber station tothe bus in the time slot assigned to the subscriber station, if thescheduling unit is able to evaluate a subscriber station number in aframe received from the bus. In this manner, using this information, thescheduling unit is able to ascertain its own time slot.

In one development of the present invention, the number of time slotsthat are assigned to the subscriber station per cycle may be at leasttemporarily unequal to a number of time slots that are assigned toanother subscriber station of the bus per cycle.

In another development of the present invention, the subscriber stationmay be designed to transmit more than one frame per time slot on thebus. Additionally or alternatively, the number of frames that thesubscriber station is allowed to transmit per time slot on the bus is atleast temporarily unequal to a number of frames that another subscriberstation of the bus is allowed to transmit per time slot on the bus.

Optionally, the communication control device is designed to transmit atthe beginning of a recessive bit in the time slot assigned to thesubscriber station a dominant pulse that is shorter than the bit time ofthe recessive bit, if the communication control device lets itstransmission opportunity elapse unused.

According to another option of the present invention, the subscriberstation is designed in such a way that the scheduling unit may beswitched on or off depending on the time requirements of thecommunication on the bus, or that an operating mode of the schedulingunit is changeable by configuration of predetermined parameters in thecontinuous operation of the bus system, the operating mode of thescheduling unit setting a predetermined mode of a communication on thebus.

At least two of the subscriber stations described above may be part of abus system, which additionally comprises a bus, the at least twosubscriber stations being connected to one another via the bus in such away that they are able to communicate serially with one another. In thiscase, at least one of the subscriber stations may be a master subscriberstation for transmitting a frame, which informs the at least twosubscriber stations of the start of a cycle of a communication on thebus,

at least one backup master being optionally provided for the additionalexecution of the function of the master subscriber station on the bus. Asubscriber station is thus able to function simultaneously as asubscriber and as a master.

The aforementioned object may additionally be achieved by a method forcommunicating in a serial bus system according to an example embodimentof the present invention. In accordance with an example embodiment ofthe present invention, the method is carried out using a subscriberstation of the bus system, which comprises a communication controldevice and a transmitting/receiving device, the method comprising thesteps of controlling, using a communication control device, acommunication of the subscriber station with at least one othersubscriber station of the bus system, and transmitting, using atransmitting/receiving device, a transmission signal generated by thecommunication control device in a frame on a bus of the bus systemaccording to the schedule of a scheduling unit, which schedules atemporal access of the subscriber station to the bus in at least onetime slot of a cycle of temporally consecutive time slots, at least onetime slot being provided in a cycle for each subscriber station of thebus for transmitting its transmission signal and the cycle repeatingcyclically, and the scheduling unit determining, by using at least oneitem of information received from the bus, an assignment that determineswhich time slot of the cycle the transmitting/receiving device may usefor transmitting the frame for the transmission signal on the bus.

The method offers the same advantages as were mentioned above withreference to the subscriber station.

Additional possible implementations of the present invention alsoinclude combinations of features or specific embodiments not explicitlymentioned above or below with regard to the exemplary embodiments. Oneskilled in the art will also add individual aspects as improvements orsupplementations to the respective basic form of the present invention,in view of the disclosure herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described below in greater detail withreference to the figures and on the basis of exemplary embodiments.

FIG. 1 shows a simplified block diagram of a bus system according to afirst exemplary embodiment of the present invention.

FIG. 2 shows a diagram illustrating the structure of messages that maybe transmitted by subscriber stations of the bus system according to thefirst exemplary embodiment of the present invention.

FIG. 3 shows a timing diagram illustrating the sequence of acommunication in the bus system according to the first exemplaryembodiment of the present invention.

FIG. 4 shows a timing diagram illustrating the sequence of acommunication in the bus system according to the first exemplaryembodiment of the present invention, after a subscriber station waswoken up again.

FIG. 5 shows a timing diagram illustrating the sequence of acommunication in a bus system according to a second exemplary embodimentof the present invention.

FIG. 6 shows a timing diagram illustrating the sequence of acommunication in a bus system according to a third exemplary embodimentof the present invention.

FIG. 7 shows a timing diagram illustrating the sequence of acommunication in a bus system according to a fourth exemplary embodimentof the present invention.

FIG. 8 shows a timing diagram illustrating the sequence of acommunication in a bus system according to a fifth exemplary embodimentof the present invention.

FIG. 9 shows a time characteristic of a differential bus signal inunused time slots in a bus system according to a sixth exemplaryembodiment of the present invention.

Unless indicated otherwise, identical or functionally equivalentelements are provided with the same reference characters in the figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows as an example a bus system 100, which is fundamentallydeveloped in particular as a CAN bus system and/or a CAN FD bus systemand/or a CAN FD successor bus system, which is here called a CAN XL bussystem, and/or variants of the same, as described below. Bus system 100may be used in a vehicle, in particular a motor vehicle, in an aircraftetc., or in a hospital etc.

In FIG. 1, bus system 100 has a plurality of subscriber stations 10, 20,30, which are respectively connected to a bus 40 having a first bus wire41 and a second bus wire 42. Bus wires 41, 42 may also be called CAN_Hand CAN_L or CAN-XL_H and CAN-XL_L and are used for electrical signaltransmission after coupling in the dominant levels or generatingrecessive levels for a signal in the transmission state. Messages 45, 46are serially transmittable via bus 40 in the form of signals between theindividual subscriber stations 10, 20, 30. If an error occurs in thecommunication on bus 40, as illustrated by the jagged black arrow inFIG. 1, an error frame (error flag) 47 may be optionally transmitted.Subscriber stations 10, 20, 30 are for example control units, sensors,display devices, etc. of a motor vehicle.

As shown in FIG. 1, subscriber station 10 has a communication controldevice 11, a transmitting/receiving device 12 and a scheduling unit 15including a counting module 151. Subscriber station 20 has acommunication control device 21, a transmitting/receiving device 22 anda scheduling unit 25 including a counting module 251. Subscriber station30 has a communication control device 31, a transmitting/receivingdevice 32 and a scheduling unit 35 including a counting module 351.Transmitting/receiving devices 12, 22, 32 of subscriber stations 10, 20,30 are each connected directly to bus 40, even if this is notillustrated in FIG. 1.

Communication control devices 11, 21, 31 are respectively used forcontrolling a communication of the respective subscriber station 10, 20,30 via bus 40 with at least one other subscriber station of thesubscriber stations 10, 20, 30 that are connected to bus 40.

Communication control devices 11, 31 generate and read first messages45, which are CAN messages for example that are constructed on the basisof a CAN XL format, which is described in more detail with reference toFIG. 2. Communication control devices 11, 31 may be additionallydesigned to provide, as needed, a Can XL message 45 or a CAN FD message46 for transmitting/receiving devices 12, 32 or to receive such from thelatter. Communication control devices 11, 31 thus generate and read afirst message 45 or a second message 46, the first and second messages45, 46 being differentiated by their data transmission standard, namely,in this case CAN XL or CAN FD.

Communication control device 21 may be developed like a conventional CANcontroller in accordance with ISO 11898-1:2015, in particular like a CANFD-tolerant classical CAN controller or a CAN FD controller.Communication control device 21 generates and reads second messages 46,for example classical CAN messages or CAN FD messages 46. The CAN FDmessages 46 may comprise a number from 0 to 64 data bytes, whichadditionally are transmitted at a markedly faster data rate than in thecase of a classical CAN message. In particular, except for unit 25,communication control device 21 is developed like a conventional CAN orCAN FD controller.

Transmitting/receiving device 22 may be developed like a conventionalCAN transceiver in accordance with ISO 11898-2:2016 or CAN FDtransceiver. Transmitting/receiving devices 12, 32 may be designed toprovide, as needed, messages 45 or bits of a frame in accordance withthe CAN XL format or messages 46 or bits of a frame in accordance withthe current CAN FD format for the associated communication controldevice 11, 31 or to receive such from the latter.

Using the two subscriber stations 10, 30, it is possible to generate andthen transmit messages 45 in the CAN XL format and to receive suchmessages 45.

FIG. 2 shows in its upper section for message 46 a CAN FD frame 460, asit is transmitted serially on bus 40 by transmitting/receiving device 12or transmitting/receiving device 22 or transmitting/receiving device 32over time t. The lower section of FIG. 2 shows for message 45 a specialexample of a CAN XL frame 450, as it may be transmitted serially on bus40 by transmitting/receiving device 22 or 32 over time t. Alternatively,the upper section of FIG. 2 may be interpreted as a classical CAN frameand the lower section of FIG. 2 may be interpreted as a CAN FD frame orCAN XL frame.

According to FIG. 2, for the CAN communication on bus 40, frames 450,460 are partitioned into different communication phases 451, 452, 453,namely, an arbitration phase 451, a data phase 452, and an end of framephase 453. In the arbitration phase 451 at the start of frame 450, 460,the associated transmitting/receiving device 12, 22, 32 transmits anidentifier 451 x and a portion of a control field. In the data phase452, the following data are transmitted inter alia: a portion of thecontrol field, the user data of the CAN XL frame or of message 45, 46 ina data field DF and a checksum. In a frame 450, a portion of the controlfield may be an optional DataType field DT, which indicates the type ofdata that are transmitted in data field DF. For illustrative purposes,DataType field DT is shown in FIG. 2 having a greater length than itoften has in relation to the length of the data field DF. DataType fieldDT may be transmitted in the control portion of the frame 450, 460, inparticular at the start of data phase 452, or at the end of arbitrationphase 451. Data phase 452 is followed by the end of frame phase 453,which also belongs to the arbitrations phase according toISO11898-1:2015. End of frame phase 453, which may also be referred toas the arbitration phase at the end of frame 450, 460, has inter aliathe following portions: an ACK field and an end of frame (EOF)indicator. The end of frame phase 453 is not relevant in this contextand is therefore not described in more detail.

In the arbitration phase 451, the associated transmitting/receivingdevice 12, 22, 32 transmits bits of frame 450, 460 at a slower bit ratethan in the data phase 452. In the case of CAN FD, the data phase 452 istemporally markedly shorter than the data phase 452 of the classical CANframe. In particular application cases, the two bit rates of phases 451,452 may be configured to the same values, but usually the bit rate inthe data phase 452 is considerably higher than in the arbitration phase451.

For CAN XL, a frame format is defined, in which not only the bit rateswithin frame 450 or message 45 are switched over, but optionally alsothe operating mode of transmitting/receiving device 12, 32. In thearbitration phase 451, transmitting/receiving device 12, 32 works in anoperating mode (here called CAN) that is compatible to ISO 11898-2:2016.In the data phase 452 of frame 450, transmitting/receiving device 12, 32may be optionally switched into another operating mode that allows forhigher bit rates and thus a fast data transmission.

The arbitration phase 451 is used to negotiate with the aid of anidentifier (ID) 451 x bitwise between subscriber stations 10, 20, 30 todetermine which subscriber station 10, 20, 30 has the message 45, 46with the highest priority and hence for the time being receivesexclusive access to bus 40 of bus system 100 for transmitting at leastin the subsequent data phase 452. For this purpose, the conventionalCSMA/CR method is applied in the arbitration phase 451, which allows forsimultaneous access of subscriber stations 10, 20, 30 to bus 40, withoutthe higher prioritized message 45, 46 being destroyed. This makes itpossible in a relatively simple manner to add further bus subscriberstations 10, 20, 30 to bus system 100, which is very advantageous.

In the arbitration phase 451, the associated transmitting/receivingdevice 12, 22, 32 thus uses a physical layer as in the case of CAN andCAN FD. The physical layer corresponds to the bit transmission layer orlayer 1 of the conventional OSI model (open systems interconnectionmodel). If scheduling units 15, 25, 35 are not activated, frames 450,460 are generated and the bus access of the individual subscriberstations proceeds in an uncoordinated manner. Conflicts in thecommunication on bus 40 are resolved by an arbitration, as defined inISO 11898-1:2015.

The CSMA/CR method has the consequence that there must be so-calledrecessive states on bus 40, which may be overwritten by other subscriberstations 10, 20, 30 having dominant states on bus 40. In the recessivestate, highly resistive conditions prevail at the individual subscriberstations 10, 20, 30, which in combination with the parasites of the buscircuit entail longer time constants. This results in a limitation ofthe maximum bit rate of today's CAN FD physical layer to currentlyapproximately 2 megabits per second in real vehicle usage.

A transmitter of message 45, 46 starts a transmission of bits of dataphase 452 on bus 40 only when the corresponding subscriber station 10,20, 30 as the transmitter won the arbitration and subscriber station 10,20, 30 as transmitter thus has exclusive access to bus 40 of bus system100 for transmitting.

Quite generally, in the bus system using CAN XL, the following deviatingproperties may be implemented in comparison to CAN or CAN FD:

-   a) take-over and, if indicated, adaptation of proven properties that    are responsible for the robustness and user-friendliness of CAN and    CAN FD, in particular the frame structure with identifier 451 x and    arbitration in accordance with the CSMA/CR method,-   b) increase of the net data transmission rate, in particular to    approximately 10 megabits per second,-   c) increase of the size of the user data per frame, in particular to    approximately 4 kbyte.

FIG. 3 shows a case for a communication on bus 40, in which schedulingunits 15, 25, 35 are activated. In this case, a deterministic bus accessof each of the subscriber stations 10, 20, 30 is possible. For thispurpose, a transmission round or cycle C is used in the communication onbus 40, in which in the simplest case one time slot S is available foreach of subscriber stations 10, 20, 30. The number SN of time slots Sthus corresponds to the number N of subscriber stations 10, 20, 30 onbus 40. The bandwidth on bus 40 is divided by the number N of subscriberstations 10, 20, 30.

In the example of FIG. 3, there are four time slots S, namely, timeslots S1, S2, S3, S4, so that four arbitrary subscriber stations ofsubscriber stations 10, 20, 30 are present. The four arbitrarysubscriber stations of subscriber stations 10, 20, 30 are thus referredto below as subscriber stations 1, 2, 3, 4.

Quite generally, SN time slots S may be provided, SN being an arbitrarynatural number. The number of time slots S is constant in the example ofFIG. 3, that is, it is the same in very cycle C. Alternatively, thenumber of time slots S may be varied, however.

There exists at least one master subscriber station on bus 40. Themaster subscriber station may be any subscriber station of subscriberstations 10, 20, 30, i.e., the subscriber station is both master as wellas normal subscriber. At the start of every cycle C, the mastersubscriber station transmits a start frame, which is referred to belowas SOCR (start of cycle frame). In one development, the SOCR is a framehaving a high priority identifier ID and a short data field DF. Inparticular, the data field DF may have the minimum length in bus system100, in particular 0 byte. All subscriber stations 1, 2, 3, 4 on bus 40synchronize to the SOCR and thereby know when they are allowed totransmit something.

Scheduling units 15, 25, 35 effect a generation of frames 450, 460according to the following rules.

Each frame 450, 460 again starts with an arbitration phase 451. Theidentifier 451 x may be chosen arbitrarily for each frame 450, 460 aslong as the rule, customary in CAN, is observed, that each identifier451 x is used exclusively only by one of subscriber stations 1, 2, 3, 4.

The minimum time slot duration T_S_mn is at least one arbitration bittime, that is, as long as the bit time of a bit in arbitration phase451. The maximum time slot duration T_S_mx is equal to the maximumlength of a frame 460 or 450. The minimum cycle duration T_C_mn is thusequal to the sum of all minimum time slot durations T_S_mn plus theminimum duration of one SOCR. Furthermore, the maximum cycle durationT_C_mx is equal to the sum of all maximum time slot durations T_S_mxplus the maximum duration of one SOCR.

Each subscriber station 1, 2, 3, 4 may transmit on bus 40 only in thetime slot S1, S2, S3, S4 that is provided for the subscriber stations 1,2, 3, 4. In the present exemplary embodiment, each subscriber station 1,2, 3, 4 may transmit a single frame 450, 460 on bus 40 in the time slotS1, S2, S3, S4 provided for it.

In its time slot S1, S2, S3, S4, each of the subscriber stations 1, 2,3, 4 respectively has one transmit opportunity TO. Thus, the subscriberstation 1, 2, 3, 4 may transmit a frame 450, 460 in the time slot S1,S2, S3, S4 assigned to it, or it may let the opportunity fortransmission elapse. Following a minimum time slot duration T_S_mn, thetransmit opportunity TO has elapsed.

In the example of FIG. 3, the minimum cycle duration T_C_mn is fourarbitration bit times plus the time duration of one SOCR, because 4 timeslots S1, S2, S3, S4 are available for the four subscriber stations 1,2, 3, 4. The minimum time slot duration T_S_mn is assumed aslarbitration bit time.

The following basic assumptions apply to the present exemplaryembodiment. In the first cycle C, that is, after the bus system 100 isswitched on, time slots S1, S2, S3, S4 are assigned to the individualsubscriber stations 1, 2, 3, 4. The assignment occurs dynamically viathe frame Ids or identifiers 451 x, which subscriber stations 1, 2, 3, 4use for transmitting their first frame 450, 460. The transmission orderis determined by the arbitration, which corresponds to the assignment oftime slots S1, S2, S3, S4 to the subscriber stations 1, 2, 3, 4.

If subscriber stations 1, 2, 3, 4 are not switched on simultaneously,the assignment of time slots S1, S2, S3, S4 is completed only when thelast subscriber station 1, 2, 3, 4 has been switched on and when everysubscriber station 1, 2, 3, 4 has transmitted a frame 450, 460. Theassignment of time slots S1, S2, S3, S4 to subscriber stations 1, 2, 3,4 is maintained in the subsequent cycles C. That is, there is no newarbitration and the transmission order remains unchanged. If one orseveral of the subscriber stations 1, 2, 3, 4 go to sleep and wake upagain, a reintegration is performed with the aid of the SOCR, whichspecifies the start of each cycle C. This will also be described in moredetail later with reference to FIG. 4. If a subscriber station hasforgotten its time slot assignment, then it is also able to integrate inthe same manner as when it is first switched on, which is describedbelow with reference to FIG. 3. In this case, the transmission order isdetermined by the utilized frame identifier 451 x and by arbitration onbus 40.

In the communication on bus 40, the SOCR is distinguishable from otherframes. This may be effected for example by using a special frameidentifier 451 x. In particular, the frame identifier 451 x has thehighest priority and thus the corresponding priority ID. This frameidentifier 451 x must then be known to all subscriber stations 1, 2, 3,4 on bus 40. Alternatively, this may also be effected for example by aspecial value in the data type field DT in the frame, which is evaluatedaccordingly by all subscriber stations 1, 2, 3, 4 on bus 40.Alternatively or additionally, a predetermined bit in the frame may beused in order to transport the information that this frame is an SOCR.Then, for example, for this predetermined bit, the value 0=no SOCR andthe value 1=SOCR. Alternatively or additionally, it is possible to use abit or byte in the data field DF for identifying the SOCR.

It is possible that the SOCR contains a varying amount of information inits data field DF. In the present exemplary embodiment, no informationis contained in the data field DF of the SOCR. Thus, in this variant, nofurther information is communicated to the subscriber stations 1, 2, 3,4 aside from the start of the next cycle C. This has the advantage thatthe SOCR uses as little communication bandwidth as possible.

FIG. 3 shows a start cycle C_SU, in which in a time duration T_C_SU, theassignment of time slots S1, S2, S3, S4 to subscriber stations 1, 2, 3,4 is determined. As mentioned previously, each cycle C starts with anSOCR. If one of the subscriber stations 1, 2, 3, 4 receives the SOCR,then this subscriber station 1, 2, 3, 4 is prepared to approve one ofthe time slots S1 through S4 for transmission, as described in moredetail below. The time slot, in which the SOCR is transmitted/received,corresponds to a time slot “S0”. For the sake of simplicity, it isassumed in the example of FIG. 3 that all subscriber stations 1, 2, 3, 4want to transmit a frame 450, 460 right at the start.

In time slot S1, all subscriber stations 1, 2, 3, 4 start a framesimultaneously and participate in the bus arbitration, as illustrated byA1234 in FIG. 3. Subscriber station 4 wins the arbitration A andtransmits its frame. This is illustrated in FIG. 3 by TX4, TX4 standingfor the transmission signal TX of subscriber station 4 and the framebeing based on transmission signal TX4. Time slot S1 is thereby assignedto subscriber station 4.

In time slot S2, subscriber stations 1, 2, 3 start a framesimultaneously and participate in the bus arbitration, as illustrated byA123 in FIG. 3. Subscriber station 2 wins the arbitration and transmitsits frame. This is illustrated by TX2 in FIG. 3. Time slot S2 is therebyassigned to subscriber station 2.

For time slot S3, an arbitration is performed between subscriberstations 1, 3, as described above. Finally, in the example of FIG. 3,time slot S3 is assigned to subscriber station 1.

Time slot S4 is assigned to subscriber station 3. An arbitration is nolonger performed because the other subscriber stations 1, 2, 4 do nottransmit anything in time slot S4.

Hence, the TX transmission order is specified by the arbitrationhereinafter as TX_4_2_1_3.

Subsequently, a normal operation of bus system 100 can begin. A possiblecycle C in the operation could be a cycle C_B, which is illustrated inFIG. 3 in the right section of the figure. In the cycle C_B, the TXtransmission order continues to be specified without change asTX_4_2_1_3. Subscriber stations 3, 4 transmit in cycle C_B. Subscriberstations 1, 2, on the other hand, do not transmit. Subscriber stations3, 4 thus make use of their transmit opportunity TO. Transmit stations1, 2, however, let their transmit opportunity TO elapse. This yields anaverage cycle duration T_C_B. The maximum cycle duration T_C_mx resultswhen in every time slot S1 through S4 the associated subscriber station1, 2, 3, 4 transmits a frame 450, 460 of the maximum length. The number1 in time slot S3 indicates that this time slot is assigned tosubscriber station 1. The number 2 in time slot S2 indicates that thistime slot is assigned to subscriber station 2. This similarly applies totime slots S1 and S4 and subscriber stations 3, 4.

For implementing the previously described scheduling for a transmissionof frames 450, 460 on bus 40, each of the scheduling units 15, 25, 35 isconstructed as described below.

Every master subscriber station 1, 2, 3, 4 on bus 40 knows the number SNof time slots S1, S2, S3, S4 per cycle C. In the simplest case, thenumber of subscriber stations 1, 2, 3, 4 on bus 40 corresponds to thenumber of time slots S1, S2, S3, S4 per cycle C, so that this yields a1-1 association of time slots and subscriber stations. The number SN oftime slots S1, S2, S3, S4 per cycle C is stored in scheduling units 15,25, 35 of the at least one master subscriber station.

Generally, any subscriber station of bus system 100 may take over thefunctions of the master subscriber station described above and below.The master subscriber station and a normal subscriber station are thusnot two separate subscriber stations. One subscriber station is thusable to assume both functions, e.g., subscriber station 1 couldadditionally also be the master subscriber station.

The normal operation for a subscriber station 1, 2, 3, 4 starts as soonas the subscriber station 1, 2, 3, 4 knows which time slot number isassigned to it. According to FIG. 3, this is the case when thesubscriber station 1, 2, 3, 4 has transmitted its first frame. Sinceevery cycle begins with an SOCR, the master subscriber station sets thecount value Scnt of counting module 15, 25, 35 to Scnt:=1 aftertransmitting the SOCR. Furthermore, every subscriber station 1, 2, 3, 4sets the count value Scnt of the counting module 15, 25, 35 of itsscheduling unit 15, 25, 35 to Scnt:=1 after receiving the SOCR. From nowon, counting module 151, 251, 351, using at least one counter, countsthe number of received frames 450, 460 on bus 40 and the number ofelapsed transmit opportunities TO. For this purpose, counting module151, 251, 351 counts per received frame 450, 460 and per elapsedtransmit opportunity TO, so that the count value Scnt of the at leastone counter is respectively incremented by 1 and thus Scnt:=Scnt+1.

As soon as the start of frame bit of a frame 450, 460 is transmitted onbus 40, counting module 151, 251, 351 counts the frame 450, 460 as atransmitted frame 450, 460 on bus 40. This also holds true if thetransmission is aborted by the transmitter, for example by an errorframe 47 due to an error.

If in the counting module 151, 251, 351 of a subscriber station for thecount value Scnt==own time slot number, the next time slot is its owntime slot. After the count value Scnt==own time slot number, thesubscriber station 1, 2, 3, 4 thus has its own transmit opportunity TOin the next time slot. Now the respective subscriber station 1, 2, 3, 4is able to transmit a frame 450, 460 or let the transmit opportunity TOelapse. Using its counting module 151, 251, 351, the master subscriberstation in this case counts from 1 through SN. Using their countingmodule 151, 251, 351, the simple subscriber stations count from 1through “own time slot number”. After that, the simple subscriberstations, more precisely their counting module 151, 251, 351, maycontinue to count or not.

If in counting module 151, 251, 351 of a master subscriber station forcount value Scnt==SN, then the next time slot is the time slot in whichthe SOCR must be transmitted. Now the master subscriber station 1, 2, 3,4 is able to transmit an SOCR frame 450, 460. If there are multiplemasters, all master subscriber stations start transmitting the SOCR inthis time slot. The arbitration ensures that the SOCR of the highestpriority prevails.

Furthermore, scheduling unit 15, 25, 35 of a subscriber station 1, 2, 3,4 memorizes the count value Scnt as its own time slot number, if thesubscriber station 1, 2, 3, 4 was able to transmit a frame. If it letsits transmit opportunity TO elapse, it keeps its own time slot numberfrom the last cycle C.

This is necessary when the transmission order on bus 40 is assigned anewand another arbitration ensues as a result. This may be the case if oneof the subscriber stations 1, 2, 3, 4 was woken up again and it thenwants to participate again in the bus communication. This is describedin more detail below with reference to FIG. 4.

After having been switched on or woken up, the subscriber stations 1, 2,3, 4 do not know which of the time slots S1, S2, S3, S4 per cycle C isassigned to the respective subscriber station 1, 2, 3, 4.

FIG. 4 shows the case in which subscriber station 3 was initially asleepand was then woken up again. The following description also applies ifmultiple subscriber stations are switched on again and simultaneouslyattempt to reintegrate.

At time t1, for example, subscriber station 3 in FIG. 4 has woken upagain and is ready to transmit. Up until this point in time and thusalso up until the point in time before subscriber station 3 was put tosleep, the transmission order was determined as TX_1_2_3_4, as shown onthe left side in FIG. 4 by the numbers in the time slots. Thereupon,subscriber station 3 waits until it receives the SOCR. Since subscriberstation 3 forgot its own time slot number, subscriber station 3 attemptsto transmit a frame after receiving the SOCR, that is, starting at timet2. Since time slot S1 is assigned to subscriber station 1, however, andsince the latter also attempts to transmit its frame, this results in anarbitration on bus 40.

In the example of FIG. 4, an arbitration therefore occurs in a time slotS1 between the frames 450, 460 of subscriber stations 1, 3, asillustrated by A13 in FIG. 4. In the example of FIG. 4, the frame ofsubscriber station 1 wins the arbitration, so that ultimately transmitsignal TX1 of subscriber station 1 is transmitted in time slot S1 andsubscriber station 1 keeps its time slot S1.

Since the frame of subscriber station 3 lost the arbitration, subscriberstation 3 repeats the transmission of its frame until the frame has wonthe arbitration and subscriber station 3 is able to transmit its frameor aborts the transmission attempt due to a bus error. Every subscriberstation 1, 2, 3, 4 is able to transmit a frame in a cycle C.

For this reason, the frames of subscriber stations 2, 3 arbitrate intime slot S2, as illustrated by A23 in FIG. 4. In the example of FIG. 4,the frame of subscriber station 2 wins the arbitration, so thatultimately transmit signal TX2 of subscriber station 2 is transmitted intime slot S2. Consequently, subscriber station 2 also keeps its timeslot S2.

In the next time slot S3, only subscriber station 3 attempts to transmitits frame. The other subscriber stations 1, 2, 4 do not transmit in timeslot S3, since time slot S3 was previously assigned to subscriberstation 3. Therefore, no arbitration occurs in time slot S3. Subscriberstation 3 is thus able to transmit its frame and has recovered its timeslot S3.

Thereupon, normal operation may also begin again for subscriber station3, since the subscriber station 1, 2, 3, 4 knows again which time slotS1, S2, S3, S4 is assigned to it, i.e., what is its own time slotnumber.

The frame identifier 451 x may be chosen arbitrarily for each frame 450,460 as long as the rule, customary in CAN, is observed, that eachidentifier 451 x is used exclusively only by one subscriber station 1,2, 3, 4. Alternatively, it is possible, however, that every subscriberstation 1, 2, 3, 4 uses only one single identifier 451 x fortransmitting all of its frames.

In deviation from the example of FIG. 4, the following holds. Ifsubscriber station 3 had used a higher priority frame identifier 451 xthan subscriber station 1, then subscriber station 3 would have beenable to transmit its frame already in time slot S1. Subscriber station 3thus would have taken over time slot S1 from subscriber station 1. Inthis case, subscriber station 1 would have been able to transmit itsframe at the latest in time slot S3, since in time slot S3 no othersubscriber station 2, 3, 4 would transmit at that time.

Depending on the result of the arbitration, this makes it possible todistribute the assignment of the time slots S1, S2, S3, S4 anew.

One advantage of this exemplary embodiment is that its implementationrequires little expenditure in the configuration. In the simplest case,in which exactly one time slot S1, S2, S3, S4 is assigned to eachsubscriber station 1, 2, 3, 4, the bus system 100 does not requireconfiguration for the described communication with the scheduling units15, 25, 35. It suffices that only the master subscriber station knowsthe number N of subscriber stations on bus 40 and thus knows the numberSN.

A further advantage of the present exemplary embodiment is that, due tothe arbitration, the communication on bus 40 is self-organizing, sincethe assignment of time slots S1, S2, S3, S4 to the subscriber stations1, 2, 3, 4 occurs dynamically via the arbitration.

The worst case delay for the bus access of a subscriber station 1, 2, 3,4 is approximately the same as in PLCA of 10BASE-T1S, namely, 2*SNmaximum frame lengths plus the frame length of the SOCR.

Furthermore, the present exemplary embodiment has in particular thefollowing advantage. If, due to an error in one of the scheduling units15, 25, 35, a subscriber station transmits in the wrong time slot, thenthis merely results in an arbitration and in a possible delay of thetransmission. Such an error, however, cannot result in the destructionof the two frames on the bus, which may result in a loss of data.

According to a modification of the first exemplary embodiment, at leastone backup master is provided. This means that even for this case thereis at least one master subscriber station on bus 40 that regularlytransmits the SOCR. The backup master also uses a fixed frame identifier451 x for the SOCR. As a result, no “single point of failure” can occur,in which no master subscriber station would be present. The at least onebackup master may be implemented by one of the subscriber stations 10,20, 30 of bus system 100.

Each backup master uses a predetermined frame identifier 451 x for theSOCR it transmits. Ideally, the frame identifiers 451 x of the backupmasters have a lower priority than the frame identifiers 451 x of themaster subscriber station.

If the master subscriber station fails, there are two possibilities asto how the at least one backup master can fill in.

According to a first variant, the master subscriber station and allbackup masters always start the SOCR simultaneously. Since the mastersubscriber station and all backup masters use different frameidentifiers 451 x and since the frame identifier 451 x of the mastersubscriber station has the highest priority, the master subscriberstation wins the arbitration. The backup masters recognize this andundertake no further SOCR transmission attempt in this cycle C. On thebasis of the frame identifier 451 x, every subscriber station 1, 2, 3, 4on bus 40 recognizes which master transmitted the SOCR.

According to a second variant, the backup masters check whether thedesignated master transmits the SOCR or does not transmit as expected.The “not transmitting” is recognized by the backup masters following theexpiration of a predetermined waiting time (timeout). The predeterminedwaiting time (timeout) is one arbitration bit time, for example.Following the predetermined waiting time (timeout), the backup mastersteps into the breach and transmits its SOCR, so that the “single pointof failure” may be avoided.

FIG. 5 shows a time sequence in bus system 100 for illustrating acommunication according to a second exemplary embodiment.

In contrast to the time sequence of the communication according to thepreceding exemplary embodiment, in the present exemplary embodiment, therespective time slot number is already predefined in a fixed manner.This is achieved in that definitively assigned time slot numbers areused on bus 40. This makes a reintegration method superfluous in thepresent exemplary embodiment, since every subscriber station 1, 2, 3, 4of bus 40 knows its assigned time slot S1, S2, S3, S4.

The assignment of the time slots may occur implicitly, time slot 1 beingassigned to subscriber station 1 for example, time slot 2 being assignedto subscriber station 2 etc., as shown for example in FIG. 5.

Alternatively, the time slots may be assigned explicitly, communicatedin particular in the SOCR.

If the assignment occurs explicitly by way of the SOCR, information istransmitted in the data field DF of the SOCR. In this connection, it ispossible that the data field DF of the SOCR contains the number SN ofthe time slots and the time slot assignment to the subscriber stationsof bus 40. Accordingly, the number SN of the time slots is communicatedto the subscriber stations 1, 2, 3, 4 with the data field DF of the SOCRin the now following cycle as well as the assignment of the time slotsto the subscriber stations of bus 40. In this case, there exists theoption that the number SN of the time slots and the time slot assignmentto the subscriber stations of bus 40 may be defined at will in eachcycle C and may thus differ in every cycle C.

For example, the number SN of the time slots in the cycle that is nowbeginning is contained in the first byte in the data field DF of theSOCR. Furthermore, the subsequent bytes in the data field DF of the SOCRmay contain the assignment of the time slots to the subscriber stationsof bus 40. Thus, for example, following byte 0, byte 1 in data field DFcontains the assignment of time slot S1 to a subscriber station number,byte 2 contains the assignment of time slot S2 to a subscriber stationnumber, etc.

This makes it possible in operation to increase or decrease in a verysimple manner the bandwidth, that is, the number and/or length of thetime slots S1, S2, S3, S4, which are guaranteed to a subscriber station1, 2, 3, 4 of bus 40. The length of the time slots S1, S2, S3, S4 ishere provided by the length of the at least one transmitted frame. It ispossible, for example, to switch to a special operating mode, inparticular flashing in a workshop, where the transmitter is granted aparticularly high bandwidth. Alternatively or additionally, a reactionto a safety emergency is possible. Such an emergency could be thefailure of a component. In such a circumstance, it is possible toprohibit a rather unimportant subscriber station from communicatingentirely or at least partially. This makes it possible to allocatebandwidth to additional frames.

Through the evaluation of the information regarding the assignment oftime slots S1, S2, S3, S4, for example from the SOCR received from bus40, the assignment of time slots S1, S2, S3, S4 in cycle C becomesvisible to the respective subscriber station 1, 2, 3, 4 of bus 40. Theprocedure is thus as follows.

In the operation of bus 40 in accordance with FIG. 5, every subscriberstation 1, 2, 3, 4 on bus 40 or, more precisely, every scheduling unit151, 251, 351 knows that a new cycle C always begins with an SOCR. Everysubscriber station 1, 2, 3, 4 on bus 40 or, more precisely, everyscheduling unit 151, 251, 351 knows which time slots S1, S2, S3, S4 isassigned to the subscriber station. Every subscriber station 1, 2, 3, 4on bus 40 or, more precisely, every scheduling unit 151, 251, 351 thusknows in which time slots S1, S2, S3, S4 the subscriber station isallowed to transmit.

Due to the fact that time slots S1, S2, S3, S4 are already assigned tosubscriber stations 1, 2, 3, 4 and that every subscriber station 1, 2,3, 4 always transmits only in its time slot, no arbitration occurs. Itis thus not necessary to distinguish between the two cases“reintegration after being switched on” and “normal operation”. Thereexists only the normal operation, which was already described withreference to the first exemplary embodiment.

According to FIG. 5, time slot S1 is assigned to subscriber station 1,time slot S2 is assigned to subscriber station 2, time slot S3 isassigned to subscriber station 3 and time slot S4 is assigned tosubscriber station 4. This is illustrated on the left side of FIG. 5.The assignment occurred e.g. by configuration of the scheduling unit.

In the example of FIG. 5, subscriber station 3 is switched on and isready at time t4 to participate in the CAN communication. Subsequently,subscriber station 3 waits for the SOCR for example. Upon receiving theSOCR, subscriber station 3 is synchronized. Subscriber station 3thereupon waits for the time slot assigned to it, that is, for time slotS3 in the example of FIG. 5. Starting at time t5, subscriber station 3is able to transmit its frame.

In the second exemplary embodiment, the subscriber station number isthus predetermined by the system integrator or by the configurator ofbus system 100. The order of the communication on bus 40 is therefore nolonger self-organizing, but rather it is predetermined, namely, via theassignment of the subscriber station number and optionally additionallyvia the information in the SOCR. The subscriber stations are then onlyallowed to transmit in a predetermined order.

This variant of an embodiment is also more robust with respect to thecounting of the time slots since the assignment of the time slots isalready firmly specified. Furthermore, the third exemplary embodimentalso has in particular the aforementioned advantage that no frame isdestroyed if due to an error in one of the scheduling units 15, 25, 35,a subscriber station transmits in the wrong time slot. Such an errormerely results in an arbitration, but not in the destruction of the twoframes on the bus.

FIG. 6 shows a time sequence in bus system 100 for illustrating acommunication according to a third exemplary embodiment.

In contrast to the time sequence of the communication according to theprevious exemplary embodiment, in the present exemplary embodiment it isalso possible that, after being switched on or woken up, a subscriberstation 1, 2, 3, 4 is even more quickly synchronized to the time slotnumber than in the previous exemplary embodiments.

Hence, in the present exemplary embodiment, a subscriber station numberis transmitted as an additional item of information in the frames 450,460. It may thus be seen on bus 40 or by evaluating the frame receivedfrom bus 40, which subscriber station 1, 2, 3, 4 of bus 40 is currentlytransmitting. Consequently, every subscriber station 1, 2, 3, 4 knowswhich subscriber station 1, 2, 3, 4 is currently transmitting and thuswhat number the current time slot S1, S2, S3, S4 has. To this end, thefollowing procedure is followed in the present exemplary embodiment.

The subscriber station number may be transmitted in different places inframe 450, 460. For example, the priority ID, which is the same as frameidentifier 451 x, may correspond to the subscriber station number ofsubscriber station 1, 2, 3, 4. Alternatively or additionally, thesubscriber station number may be transmitted in the data field DF or viathe DataType field DT.

In the example of FIG. 6, the assignment of time slots S1, S2, S3, S4 tosubscriber stations 1, 2, 3, 4 may be seen on the left side of FIG. 6.Time slot S1 is assigned to subscriber station 1 etc., and time slot S4is assigned to subscriber station 4.

Subscriber station 3 is switched on and in the example of FIG. 6 isready at time t6 to participate in the CAN communication. Subsequently,subscriber station 3 waits for the SOCR or for a different frame, inorder to synchronize to the time slot numbers. At time t7, subscriberstation 3 has received a frame from subscriber station 2. As soon assubscriber station 3 has received the subscriber station numbertransmitted in the frame of subscriber station 2, subscriber station 3knows that the time slot that has just elapsed is time slot S2.Subscriber station 3 is thereby synchronized to the time slot numbers.Since in this example time slot S3 follows immediately afterwards, thesubscriber station is able to transmit its frame in time slot S3 withtransmission signal TX3. If subscriber station 2 had let its transmitopportunity TO elapse, subscriber station 3 would have received the SOCRa few bits later and would thus also be synchronized to the time slotsS.

It is very advantageous in the third exemplary embodiment that onaccount of the subscriber station number transmitted in time slot S1,S2, S3, S4, a subscriber station 1, 2, 3, 4 that has been switched onagain or woken up is synchronized more quickly to the firmly assignedtime slot numbers S1, S2, S3, S4 or to the time slot numbers S1, S2, S3,S4 present in the communication on bus 40 than in the previous exemplaryembodiments. The worst case delay for the bus access of a subscriberstation 1, 2, 3, 4 is thus reduced to 1*SN maximum frame lengths plusthe frame length of the SOCR. The worst case delay is thus shorter byapproximately half than in the preceding exemplary embodiments.

This variant of an embodiment is also more robust with respect to thecounting of the time slots since the time slot number may be seen on bus40. Furthermore, the present exemplary embodiment also has in particularthe aforementioned advantage that no frame is destroyed if due to anerror in one of the scheduling units 15, 25, 35, a subscriber stationtransmits in the wrong time slot. Such an error merely results in anarbitration, but not in the destruction of the two frames on the bus.

FIG. 7 shows a time sequence in bus system 100 for illustrating acommunication according to a fourth exemplary embodiment. For thispurpose, FIG. 7 shows in its left section a cycle having a minimum cycletime duration T_C_mn, in which all time slots S1 through S4 respectivelyhave at least two arbitration bit times. For example, time slot S3 has afirst bit time B1_S3 and a second bit time B2_S3. The same is true forthe other time slots S1, S2, S4.

A subscriber station 1, 2, 3, 4, which has its transmit opportunity TOin a time slot S1, S2, S3, S4, must start its frame in the first bit ofthe time slot S1, S2, S3, S4 assigned to it, in order to be guaranteedto be able to transmit a frame. Thus, no bit elapses in time slot S1,S2, S3, S4. If a subscriber station 1, 2, 3, 4 lets the first bit of itstime slot S1, S2, S3, S4 elapse, then the subscriber station 1, 2, 3, 4has also let its transmit opportunity TO elapse, which would haveguaranteed the subscriber station 1, 2, 3, 4 the transmission of aframe. Thus, subscriber station 1, 2, 3, 4 currently does not want totransmit a frame.

Consequently, another subscriber station 1, 2, 3, 4 is now able to usethis time slot S1, S2, S3, S4 for transmission. It is possible, however,that for example the subscriber station 1 lets its first bit time B1_S1of its time slot S1 elapse, but then actually begins to transmit a framein the second bit time B2_S1 of its time slot S1. In this example, it isthus possible for all subscriber stations 1, 2, 3, 4 to start a frame inthe second bit time B2_S1 of time slot S1. The frames may also “fight”over this free time slot S1, that is, arbitrate on bus 40. In order forthe frame having the highest priority to win the arbitration, subscriberstations 1, 2, 3, 4 may use identifiers 451 x for their frames thatbegin in the second bit of a time slot, which match the priority of theframe. The arbitration ensures that the frame of the highest priorityprevails.

This development of the minimum duration T_S_mn of time slots S1 throughS4 makes it possible for one of the subscriber stations 1, 2, 3, 4 touse the transmit opportunity TO of another subscriber station, becauseit is clear from a first bit time that elapsed unused that therespective subscriber station has not used its guaranteed transmitopportunity TO.

In the example of FIG. 7, subscriber station 4 uses the fourth time slotS4 that is assigned to it for transmitting the transmission signal TX4in a frame. At a time t8 during time slot S4, subscriber station 3 isready to transmit a frame. Since subscriber station 1 does not transmita frame—the first bit time B1_S1 elapsing unused—starting at time t9,subscriber station 3 transmits the transmission signal TX3 as a frame inthe second bit time B2_S1 of time slot S1. The second and third timeslots S2, S3 are respectively used by the associated subscriber stations2, 3. Transmit signals TX2, TX3 are thus respectively transmitted in aframe on bus 40. Since subscriber station 4 does not transmit aframe—the first bit time B1_S4 elapsing unused—subscriber stations 1, 2transmit frames on bus 40 starting at time t10. In the subsequentarbitration, subscriber station 2 prevails, so that transmission signalTX2 is transmitted as a frame on bus 40 in time slot S4.

One advantage of the present exemplary embodiment is that it is possibleto mix a deterministic allocation of the communication bandwidth with abest effort data traffic. The best effort data traffic only comes aboutif some subscriber stations 1, 2, 3, 4 do not use the bandwidth, thatis, the transmission slot S1, S2, S3, S4, allocated to them.

Another great advantage of the present exemplary embodiment is that theworst case delay for the bus access increases thereby only minimally.The time delay increases minimally because the subscriber stations firstwait one bit time before they use another time slot.

In principle, the minimum time slot duration T_S_mn may alternativelyhave a length of three or more arbitration bit times. Subscriberstations 1, 2, 3, 4 on bus 40 may then be divided into differentpriority classes. The lower the priority class of a subscriber station1, 2, 3, 4, the later the subscriber station 1, 2, 3, 4 may start atransmission within a time slot that remains free.

According to a modification of the present exemplary embodiment, thedevelopment having at least two bit times may be used so that subscriberstations 1, 2, 3, 4, after waking up or being switched on, arereintegrated in such a way that a transmitting subscriber station 1, 2,3, 4 is not disadvantaged in that the time slot S1, S2, S3, S4 assignedto it is taken away from the transmitting subscriber station 1, 2, 3, 4.For this purpose, preferably every subscriber station 1, 2, 3, 4 usesfor reintegration only time slots S1, S2, S3, S4 that were not used inthe first bit by the actual time slot owner. If the reintegratingsubscriber station of the subscriber stations 1, 2, 3, 4 transmits itsframe starting with the second bit of time slot S1, S2, S3, S4 and if itwins the arbitration and is able to transmit the frame successfully,that is, error-free, then the time slot is subsequently assigned to it.

FIG. 8 shows a time sequence in bus system 100 for illustrating acommunication according to a fifth exemplary embodiment.

In contrast to the preceding exemplary embodiments, in the presentexemplary embodiment, the communication bandwidth on bus 40 is notuniformly distributed between subscriber stations 1, 2, 3, 4. Instead,in the present exemplary embodiment, a so-called WRR method (weightedround robin method) is used. In the process, each subscriber station 1,2, 3, 4 obtains a further parameter W (weight), which is adjustable inthe associated scheduling unit 15, 25, 35 during the configuration. Theparameter W indicates the number of frames 450, 460, which thesubscriber station 1, 2, 3, 4 may transmit per cycle. W time slots areprovided for one subscriber station 1, 2, 3, 4. For this reason, theparameter SN set in the at least one master subscriber station now nolonger corresponds to the number of subscriber stations 1, 2, 3, 4, butrather to the sum of all values of parameter W.

FIG. 8 shows an example with four subscriber stations 1, 2, 3, 4, inwhich the parameter W=2 is set for subscriber station 1. For the othersubscriber stations 2, 3, 4, on the other hand, a parameter W=1 isrespectively set. The number SN of time slots thus computes asSN=2+1+1+1=5. Consequently, a cycle C has a number of 5 time slots,namely, S1, S2, S3, S4, S5. In this case, subscriber station 1 is ableto transmit two frames 450, 460 per round, namely, in time slots S1 andS2. The other subscriber stations 2, 3, 4 are each able to transmit onlyone frame 450, 460 per cycle C.

For explaining a sixth exemplary embodiment, FIG. 9 shows a differentialvoltage V-diff, which is computed from the difference of bus signalsCAN_H and CAN_L on bus 40.

According to FIG. 9, a subscriber station 1, 2, 3, which is not usingits transmit opportunity TO, transmits a short dominant pulse P at thebeginning of bits B1_S1, B1_S2, B1_S3, etc., in its time slot S1, S2,S3. In the example of FIG. 9, only one bit, namely, the bit B1, istransmitted in each time slot S1, S2, S3, since the minimum time slotduration T_S_mn is assumed here to be an arbitration bit time. The bitsare scanned by the receiving subscriber stations 1, 2, 3 at a scanningtime t_A. If the minimum duration T_S_mn of a time slot corresponds tomultiple arbitration bit times, then the subscriber station, to whichthe time slot is assigned, is able to transmit a dominant pulse P at thebeginning of each bit if the subscriber station lets its transmitopportunity TO elapse.

In this case, the associated subscriber station 1, 2, 3 transmits adominant pulse P of e.g. 200 ns in the recessive bits of its time slotS1, S2, S3. All CAN subscriber stations 1, 2, 3 synchronize to therecessive-dominant edge S_F of the dominant pulse P. Since thearbitration bit time is limited to 1000 ns or 1 Mbit/s in accordancewith the aforementioned specification, a corresponding pulse P of 200 nsis not limiting. All subscriber stations 1, 2, 3 scan the actuallyrecessive bit B1 as recessive in spite of the dominant pulse P, becauseat scanning time t_A, the pulse P has already ended long ago.

This makes it possible that subscriber stations 1, 2, 3 do not lose thesynchronization to time slots S1, S2, S3, even if long idle phases occurin the communication on bus 40, in which all subscriber stations 1, 2, 3do not use their transmit opportunities TO. By way of the dominantpulses P, subscriber stations 1, 2, 3 may be kept synchronized.

Bus system 100 is thus able to handle clock pulses that have relativelyhigh tolerances. In this case, subscriber stations 1, 2, 3 synchronizeto recessive-dominant edges on bus 40.

According to a seventh exemplary embodiment, it is possible that one ormultiple subscriber stations 1, 2, 3, 4 of the preceding exemplaryembodiments transmit multiple frames per time slot S1, S2, S3, S4. Thisdevelopment is advantageous for example in order to distribute thecommunication bandwidth on bus 40 more fairly, when for examplesubscriber station 1 typically transmits short frames 460 and subscriberstation 2 typically transmits long frames 450. If each subscriberstation 1, 2 is always only able to transmit one frame in the time slotS1, S2 assigned to it, then subscriber station 1 has less bandwidth thansubscriber station 2 in the method according to the first through thethird exemplary embodiment.

In order to achieve greater fairness with regard to the communicationbandwidth than in the first through the third exemplary embodiments,subscriber station 1 is for example permitted to transmit multiple shortframes 450 during its time slot S1. In order to remain fair, frames 450in sum total should not be longer than a frame 450 of maximum length.

The fact that an additional frame 460 is transmitted by subscriberstation 1 in this transmit opportunity TO may be signaled in thefollowing ways.

For example, an identifier 451 x may be used for this purpose. In thiscase, the less significant 4 bits of the identifier (ID) 451 x are usedto identify subscriber station 1. The next 7 bits of identifier (ID) 451x are used to communicate that additional frames 460 will follow. 0x14,for example, may signal that subscriber station 4 transmits a frame, the1 signaling that the frame is followed by additional frames. 0x04 couldthen signal that subscriber station 4 transmits a frame, the 0 signalingthat the frame is not followed by additional frames.

According to another possibility for signaling that subscriber station 1will still transmit a frame 450 in this transmit opportunity TO, a fieldDataType (DT) may be used in the header of frame 450. DT=0x30, forexample, may signal that no additional frame of the same subscriberstation follows. DT=0x31 could therefore signal that one additionalframe of the same subscriber station follows.

Alternatively, according to yet another possibility for signaling, it ispossible to use a dedicated bit in the header of frame 460.

Alternatively, according to yet another possibility for signaling, it ispossible to use a bit or byte at the beginning of the data field DF,shown in FIG. 2, in the data phase 452.

The advantage is that more fairness may be established with regard tothe distribution of the communication bandwidth between subscriberstations 1, 2, 3, 4 in the case in which subscriber stations 1, 2, 3, 4transmit frames 450, 460 of different lengths.

According to an eighth exemplary embodiment, it is possible that thenumber SN of the time slots is set in the scheduling units 15, 25, 35 tobe greater than the number N of subscriber stations. In this case, atleast one time slot remains, which belongs to none of the subscriberstations and thus to no one on bus 40. If this is combined with thefourth exemplary embodiment, where it is explained how the othersubscriber stations are able to use unused time slots, then the surplustime slots may be used by any subscriber station.

Since in principle all subscriber stations may transmit simultaneouslyin the surplus time slots and thus arbitrate over bus 40, thiscorresponds to strict priority scheduling.

The bus has N=4 subscriber stations, for example, that is, thesubscriber stations 1, 2, 3, 4, and SN=5 time slots, that is, the timeslots S1, S2, S3, S4, S5. One time slot is assigned to each subscriberstation exclusively. Since in time slot S5, a node will never transmitimmediately, the nodes are able to arbitrate over time slot S5 startingwith the second bit of the time slot.

Alternatively, this eighth exemplary embodiment may also be implementedas an extension of the second or third exemplary embodiment. Schedulingunits 15, 25, 35 not only have the number SN of time slots configured,but also the number of time slots that are available to all subscriberstations, for example at the end of cycle C. If the time slots arefirmly assigned to the subscriber stations as in the second and thirdexemplary embodiments, the time slot number is optionally contained inthe transmitted frame and an SOCR marks the start of a cycle C, then ascheduling unit is able to detect the time slot S5 (from the previousexample). When time slot S5 has arrived, all subscriber stations maysimply arbitrate here over bus 40. The combination with the fourthexemplary embodiment is no longer necessary.

Since every one of subscriber stations 1, 2, 3, 4 is able to transmit intime slot S5, the allocation of transmit opportunity TO in time slot S5is strictly in accordance with the priority, that is, the identifier 451x of the frames, which the subscriber stations 1, 2, 3, 4 transmit intime slot S5 (strict priority scheduling). The frame identifier 451 x ofmessages 450, 460 is to be selected in this time slot S5 expediently inaccordance with the actual priority of the messages, so that the framehaving the highest priority is able to prevail.

According to a ninth exemplary embodiment, it is possible to eliminatethe arbitration phase 451 in the communication entirely or at leastpartially. As a result, in normal operation, even in the first exemplaryembodiment, in deterministic scheduling using scheduling units 15, 25,35, there is no arbitration, because one or multiple time slots S1, S2,S3, S4 are assigned to every subscriber station 1, 2, 3, 4.Consequently, following the assignment of the time slots S1, S2, S3, S4or at this operating point, the arbitration phase 451 may be omittedentirely or at least partially prior to and following the data phase452.

As a result, the arbitration phase 451 is now shorter than in CAN, thatis, shorter than currently defined in ISO 11898-1:2015.

In such a case, the following two operating modes exist. In a firstoperating mode, upon being switched on, all subscriber stations 1, 2, 3,4 use normal CAN frames or CAN XL frames, because arbitration may occuron the bus. As soon as all subscriber stations 1, 2, 3, 4 are inoperation and all subscriber stations 1, 2, 3, 4 are synchronized totime slots S1, S2, S3, S4, arbitration will consequently no longeroccur. For this reason, the system may now be switched into the secondoperating mode, in which the arbitration phase 451 is omitted entirelyor at least partially.

This makes it possible to avoid the case that the arbitration phase 451and the frame end phase 453 with their relatively long bits, which aresituated before and after the data phase 452, results in a relevantoverhead in the data transmission on bus 40 and thus in a lower net datarate.

According to a tenth exemplary embodiment, it is possible that theidentifiers 451 x, which are used for transmitting the frames 450, 460,are divided into two ranges. First, into a high priority range, which isused for those frames 450, 460 that are transmitted by a subscriberstation in the time slot assigned to the subscriber station. And second,into a low priority range, which is used for those frames that aretransmitted in a time slot that is not exclusively assigned to thetransmitting subscriber station.

In order to attempt to use a time slot that is exclusively assigned toanother subscriber station, subscriber station 1 for example, to whichfor example the currently present time slot S3 is not exclusivelyassigned, must simply use an identifier 451 x from the low priorityrange when attempting to transmit frame 450, 460. This ensures that forexample subscriber station 3, to which in this example the currentlypresent time slot S3 is exclusively assigned, would always win thearbitration and that thus this time slot S3 remains exclusively assignedto subscriber station 3. If, however, in this example at least one ofthe other subscriber stations 1, 2, 4 has something to transmit, thenthis other subscriber station 1, 2, 4 may attempt right at the beginningof time slot S3 to transmit a frame 450, 460 with an identifier 451 xfrom the low priority range.

This has the advantage that in the present exemplary embodiment theminimum time slot duration T_S_mn remains at an arbitration bit time,whereas in the fourth exemplary embodiment the minimum time slotduration T_S_mn amounts to two arbitration bit times.

All the previously described developments of subscriber stations 1, 2,3, 4, 10, 20, 30 of bus system 100 and the methods carried out thereinmay be used individually or in all possible combinations. In particular,all features of the previously described exemplary embodiments and/or oftheir modifications may be combined in any manner. Additionally oralternatively, particularly the following modifications are possible.

Although the present invention was described above with reference to theexample of the CAN bus system, the present invention may be used in anycommunication network and/or communication method. In particular, twodifferent communication phases may be used in the communication networkand/or communication method, as described above with reference to thecommunication phases 451, 452.

In particular, bus system 100 according to the exemplary embodiments maybe a communication network, in which data are serially transmittable attwo different bit rates. It is advantageous, but not an unavoidablepresupposition, that in bus system 100, at least for certain timeperiods, exclusive, collision-free access by a subscriber station 10,20, 30 to a common channel is ensured.

The number and the arrangement of the subscriber stations 10, 20, 30 inbus systems 100 of the exemplary embodiments is a matter of choice. Inparticular, subscriber station 20 in bus system 100 may be omitted. Itis possible that one or multiple subscriber stations 10 or 30 exist inbus system 100. It is possible that all subscriber stations in bussystem 100 are developed identically, that is, that only subscriberstations 10 or only subscriber stations 30 exist.

The deterministic scheduling performed by scheduling units 15, 25, 35may be switched on or switched off at any time so as to adapt to thecurrent operating states of bus system 100. In real-time operation, forexample, the deterministic scheduling is used. The deterministicscheduling may be switched off, on the other hand, in a workshop whenflashing new firmware versions.

Additionally or alternatively, it is possible that in an operation ofthe deterministic scheduling, the previously described parameters SN, W,which are used by scheduling units 15, 25, 35, may be changed as desiredin continuous operation.

1-20. (canceled)
 21. A subscriber station for a serial bus system, comprising: a communication control device configured to control a communication of the subscriber station with at least one other subscriber station of the bus system; a transmitting/receiving device configured to transmit a transmission signal generated by the communication control device in a frame on a bus of the bus system; and a scheduling unit configured to plan a temporal access of the subscriber station to the bus in at least one time slot of a cycle of temporally consecutive time slots, at least one time slot being provided in the cycle for each subscriber station of the bus for transmitting its transmission signal and the cycle being repeated cyclically, wherein the scheduling unit is configured to determine, by using at least one item of information received from the bus, an assignment that specifies which time slot of the cycle the transmitting/receiving device may use for transmitting the frame for the transmission signal on the bus.
 22. The subscriber station as recited in claim 21, wherein the at least one item of information received from the bus is a frame communicating a start of the cycle, and the at least one item of information received from the bus additional includes a frame identifier and/or an assignment of the time slots of the cycle to the subscriber stations of the bus and/or information as to which of the subscriber stations of the bus is currently transmitting.
 23. The subscriber station as recited in claim 22, wherein the scheduling unit is configured to use, as the at least one item of information received from the bus, at least the frame informing of a start of the cycle and to evaluate a frame identifier of a transmitter of a frame received from the bus.
 24. The subscriber station as recited in claim 22, wherein the scheduling unit is configured to evaluate a data field of the frame informing of the start of the cycle, in which the at least one item of information received from the bus is contained.
 25. The subscriber station as recited in claim 21, wherein the scheduling unit is configured to wait until the communication control device has received from the bus a frame informing of the start of the cycle and is configured to subsequently determine, together with other subscriber stations of the bus in an operation of the bus system by using a priority of the transmission signal, which time slot of the cycle the transmitting/receiving device may use for transmitting the frame for the transmission signal on the bus.
 26. The subscriber station as recited in claim 21, wherein the communication control device is configured to partition the frame into a first communication phase and a second communication phase at least in a switch-on phase of the bus, and in the first communication phase, a negotiation takes place to determine which of the subscriber stations of the bus is granted an at least temporarily exclusive, collision-free access to the bus in a subsequent second communication phase.
 27. The subscriber station as recited in claim 26, wherein a number of the time slots per cycle is greater than a number of time slots, which are assigned to the subscriber stations of the bus per cycle, and in a time slot which is not assigned to any of the subscriber stations of the bus, in the first communication phase, the negotiation takes place to determine which of the subscriber stations of the bus is granted an at least temporarily exclusive, collision-free access to the bus in the subsequent second communication phase.
 28. The subscriber station as recited in claim 26, wherein a minimum duration of a time slot is a bit time of a bit of the first communication phase, and the scheduling unit is configured to transmit, in a time slot assigned to the subscriber station, a frame having a priority that is higher than a priority of a frame which the scheduling unit is configured to transmit in a time slot that is assigned to another subscriber station of the bus.
 29. The subscriber station as recited in claim 26, wherein a minimum duration of a time slot is two bit times of a bit of the first communication phase, and wherein the scheduling unit is configured to approve a temporal access of the subscriber station to the bus in a second bit of the time slot of the cycle when another subscriber station of the bus lets its transmit opportunity elapse unused in a first bit of the time slot.
 30. The subscriber station as recited in claim 21, wherein the scheduling unit includes a counting module which is configured to increment its count value with each frame received from the bus and to increment it with each transmit opportunity that has elapsed unused for a time slot, and the counting module is configured to set its count value to 1 when a frame informing of a start of the cycle is received.
 31. The subscriber station as recited in claim 30, wherein the counting module is configured to increment its count value with every frame received from the bus following reception of a bit which signals a beginning of a frame, even if the frame is later aborted, by a subscriber station that transmitted the frame, due to an error.
 32. The subscriber station as recited in claim 30, wherein the scheduling unit is configured to approve a temporal access of the subscriber station to the bus for a next time slot of the cycle when the count value of the counting module is equal to the number of the time slot that is assigned to the subscriber station.
 33. The subscriber station as recited in claim 21, wherein the scheduling unit is configured to approve a temporal access of the subscriber station to the bus in a time slot of the cycle when the subscriber station or another subscriber station of the bus lets its transmit opportunity elapse unused.
 34. The subscriber station as recited in claim 21, wherein the communication control device is configured to include a subscriber station number in the transmission signal which is assigned exclusively to the subscriber station on the bus, and the scheduling unit is configured to approve a temporal access of the subscriber station to the bus in the time slot assigned to the subscriber station when the scheduling unit is able to evaluate a subscriber station number in a frame received from the bus.
 35. The subscriber station as recited in claim 21, wherein a number of time slots which are assigned to the subscriber station per cycle is at least temporarily unequal to a number of time slots which are assigned to another subscriber station of the bus per cycle.
 36. The subscriber station as recited in claim 21, wherein the subscriber station is configured to transmit per time slot more than one frame on the bus, and/or a number of frames which the subscriber station is allowed to transmit per time slot on the bus, is at least temporarily unequal to a number of frames which another subscriber station of the bus is allowed to transmit per time slot on the bus.
 37. The subscriber station as recited in claim 21, wherein the communication control device is configured to transmit at a beginning of a recessive bit in the time slot assigned to the subscriber station a dominant pulse that is shorter than a bit time of the recessive bit if the communication control device lets its transmit opportunity elapse unused.
 38. The subscriber station as recited in claim 21, wherein the subscriber station is configured in such a way that the scheduling unit may be switched on or off depending on time requirements of the communication on the bus, or that an operating mode of the scheduling unit is changeable by configuration of predetermined parameters in a continuous operation of the bus system, the operating mode of the scheduling unit setting a predetermined mode of a communication on the bus.
 39. A bus system, comprising: a bus; at least two subscriber stations connected to one another via the bus in such a way that they are able to communicate with one another serially, each of the at least two subscriber stations including: a communication control device configured to control a communication of the subscriber station with at least one other subscriber station of the bus system, a transmitting/receiving device configured to transmit a transmission signal generated by the communication control device in a frame on a bus of the bus system, and a scheduling unit configured to plan a temporal access of the subscriber station to the bus in at least one time slot of a cycle of temporally consecutive time slots, at least one time slot being provided in the cycle for each subscriber station of the bus for transmitting its transmission signal and the cycle being repeated cyclically, wherein the scheduling unit is configured to determine, by using at least one item of information received from the bus, an assignment that specifies which time slot of the cycle the transmitting/receiving device may use for transmitting the frame for the transmission signal on the bus; wherein at least one of the subscriber stations is a master subscriber station configured to transmit a frame which informs the at least two subscriber stations of a start of the cycle of a communication on the bus.
 40. The bus system as recited in claim 39, further comprising at least one backup master for additional execution of a function of the master subscriber station on the bus.
 41. A method for communicating in a serial bus system, the method being carried out using a subscriber station, of the bus system, which includes a communication control device and a transmitting/receiving device, the method comprising the following steps: controlling, using a communication control device, a communication of the subscriber station with at least one other subscriber station of the bus system; and transmitting, using a transmitting/receiving device, a transmission signal, generated by the communication control device, in a frame on a bus of the bus system in accordance with a scheduling of a scheduling unit, which schedules a temporal access of the subscriber station to the bus in at least one time slot of a cycle of temporally consecutive time slots, at least one time slot being provided in the cycle for each subscriber station of the bus for transmitting its transmission signal and the cycle being repeated cyclically, and the scheduling unit determining, by using at least one item of information received from the bus, an assignment that specifies which time slot of the cycle the transmitting/receiving device may use for transmitting the frame for the transmission signal on the bus. 